In lenticular imaging, an optical element called a lenticular screen is placed between an image and the viewer, as disclosed, for example, in U.S. Pat. Nos. 3,504,059 to Glenn, Jr.; 2,724,312 to Gruetzner; and 3,683,773 to Dudley. Lenticular screens are typically formed from a transparent plastic sheet with lenses integrally formed on only one side that focus on the opposite and typically flat side. The lenticular elements can have many shapes, such as, for example, cylindrical, angular, spherical, or shaped like cube corners.
The original lenticular image can be created photographically, electronically or by a combination of both. Images can be reproduced and mass produced using photo-sensitive materials, printed by lithographic means or by other means of printing or transfer of inks or dyes. Electronic displays, such as cathode-tubes or flat panel displays, may also be fitted with a lenticular screen if the resolution of the display is sufficient.
One known technique for manufacturing lenticular screens includes cutting the lenticular lens pattern directly into transparent plastic materials. A lenticular screen can also be formed by the casting of thermosetting resins onto flat forms including the lenticular lens pattern. In addition, a lenticular screen may also be made by thermoforming a cast or extruded transparent sheet by heat and pressure between one polished plate and one plate with the lenticular pattern cut or engraved into its surface. Injection molding may also be used to form a lenticular screen.
A lenticular screen may also be formed by extrusion of resin onto transparent pre-produced sheet or film, wherein the lenticular pattern is embossed into the resin by an embossing roll. The applied resin may then be cured by radiation through the transparent material while the web is in contact with the embossing roller. Alternately, if the properties of the resin permit, the resin may be cured by radiation after the sheet has left the embossing roll.
A lenticular screen may also be manufactured using a machine similar to that normally used for flat sheet extrusion. As disclosed in U.S. Pat. No. 2,724,312 to Gruetzner, for example, and as shown with reference to the prior art illustration of FIG. 1, such a machine 20 includes a sheet extruder 21 and a polishing stack 22. The polishing stack 22 illustratively includes three rolls 23, 24 and 25, wherein the middle roll 24 has the lenticular pattern on its outer surface. The upper roll 23 and lower roll 25 have a smooth outer surface. A plurality of small rolls 27 support the sheet 26, and a pair of pull rolls 28 pull the sheet from the polishing stack 22. This type of machine 20 and associated method are used for most of the lenticular sheet produced at present.
The lenticular image can be reproduced on the photographic material and thereafter be laminated to the lenticular screen. There are also applications where the photographic emulsion is coated onto the flat side of the screen. The lenticular image can also be printed with inks or dyes on a suitable material which, in turn, is laminated to the back of the screen or printed directly onto the flat side of the screen. Common for all the processes are that the lenticular image and the lenticular screen meet exacting tolerances to obtain the desired result.
The three roll polishing stack 22 is basically a simplified calendar. The polishing rolls 23, 24 and 25, are also known as chill rolls in flat plastic sheet production or as embossing rolls, if a pattern is cut or engraved into their surface. The functions of the rolls are to give the sheet, which initially is pre-formed by the sheet die at the end to the extruder 21, a more uniform gage, polish the sheet surface, transfer the pattern of the embossing roll to the sheet, and chill the material to a temperature lower than its softening point to keep the sheet in the shape formed by the rolls. The embodiment of the prior art machine 20' of FIG. 2 illustrates that the rolls 23', 24' and 25' can be arranged in a diagonal orientation. Of course a horizontal orientation is also possible.
Yet another difficulty with conventional machines for making lenticular screen is that production of the polishing rolls may be elaborate and costly. A common conventional technique for fabricating a polishing roll applies a hard chrome plating for wear and corrosion resistance onto a steel mantel. The chrome layer is then polished to meet the exacting tolerances needed. Unfortunately, the entire polishing roll must be removed when worn, shipped to a remote site for refinishing, and transported back for re-installation. The roll is relatively bulky and, thus, costly to ship. In addition, the machine may be out of service while the roll is being refinished or replaced.